Tumor hypoxia is an obstacle to optimal treatment with radiotherapy and for many chemotherapeutic agents. Experimentally, it has been found that perfluorocarbon - oxygen breathing - can correct tumor hypoxia and that such treatment can substantially improve the anti-tumor effect of radiotherapy and chemotherapy. Using the Eppendorf pO2 histograph, we plan to evaluate human tumors, specifically head and neck cancer, metastatic breast cancer, and metastatic melanoma for hypoxia. A phase I - phase II clinical pharmacologic study of fluosol-oxygen will be conducted in these patients wherein a critical endpoint will be correction of hypoxia. Finally, the patients will be treated with chemotherapy during the perfluorocarbon oxygen breathing. If the aforementioned studies prove positive, appropriate phase II and phase III studies will be conducted. In parallel with the above, studies will be conducted in a rat transplanted breast cancer model to provide leads and course correction for the clinical study, as well as to provide more fundamental information with respect to hypoxia and its perturbation.